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Project Introduction

A small Mars (or other celestial body) ascent vehicle is unlikely to achieve the necessary propellant fraction required to achieve orbit. Scaling down of liquid propulsion systems, as shown in the figure, is difficult. In the 100-kg class of vehicles, liquid propellant vehicle designers should expect a propellant fraction of only 0.75. In contrast, solid rocket motors (SRM) scale down much easier, so designers should expect a propellant fraction of at least 0.92. To be practical, however, the SRM must operate in extreme low temperature environments, which is difficult for state of the art polybutadiene binders. ASI proposes to develop a new, low temperature binder based upon siloxane. Siloxane polymers have glass transition temperatures below 150K, making them ideal for use on Mars with little or no external heaters required. A siloxane binder SRM-based MAV will easily achieve the propellant fraction needed for a sample return mission.
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Anticipated Benefits

Our primary technology insertion opportunity within NASA is the Mars Sample Return (MSR) mission. The Mars climate enforces a uniquely stressing environment that every propulsion system must deal with. However, we are also aware that NASA is focusing upon spacecraft and lander missions to asteroids and other near-earth bodies that will require operating at extreme low temperatures approaching -270�Ca scant 3�C above absolute zerothat will test the limits of every known material. From a propulsion system perspective, such missions demand, to an even greater extent than MSR, the kind of performance siloxane binders appear to offer. We are not aware of any polymer with a glass transition temperature near the liquid temperature of helium, so these missions will require electric heaters for the motor. Siloxane binders would reduce the power requirements for such spacecraft. Other potential NASA uses will be in the Space Launch System (SLS) program, perhaps used as ullage settling motors (USM), tower jettison motors, or even crew escape system motors. We are aware, of course, that motor designs currently exist (and have been tested) for these uses, but there may come a time when the additional structural margin at low launch temperatures is needed. Siloxane binders can fill that need.
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